feat(Order/Bounds/Lattice): Bounds over collections of sets

[mans0954]

Some results about upper and lower bounds over collections of sets.

Inspired by #15412, but possibly of greater interest?

---

[github-actions]

PR summary d33d8dec63

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.Order.Bounds.Lattice	357

---

Declarations diff

+ IsGLB.iUnion
+ IsLUB.iUnion
+ lowerBounds_iUnion
+ upperBounds_iUnion

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

The doc-module for script/declarations_diff.sh contains some details about this script.

---

No changes to technical debt.

You can run this locally as

./scripts/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).